Stannous complexes and their preparation



Patented Jan. 27, 1953 STANNOUS COMPLEXES AND THEIR PREPARATION Harry E. Albert, Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application April 4, 1949, Serial No. 85,473

13 Claims. 1

This invention relates to the stabilization of rubbers and, more particularly, rubber-like copolymers of a conjugated diene monomer and a vinyl aromatic monomer, typified by GR-S. The conjugated diene monomers which may be used in such copolymers include butadiene (by which is meant the compound butadiene 1-3), isoprene, 2-cyanobutadiene, cyclopentadiene, piperylene, dimethyl-butadiene, 2-methyl 1 ,3 pentadiene, etc. The vinyl aromatic monomers include styrene, nuclear-substituted styrenes, alphamethylstyrene, monochlorostyrene, dichlorostyrene, vinylnaphthalene, vinylbiphenyl, vinylcarbazole, 2-vinyl-5-ethylpyridine, 2-ethyl-5- vinylpyridine, etc. The invention includes the new stabilizers, their use in the rubber-like copolymers, and the stabilized products.

The stabilizers most generally used with such a copolymer, such as the well-known phenylbeta-naphthylamine, on aging discolor the copolymer and light-colored vulcanizates prepared from the copolymer. These light-colored vulcanizates are badly discolored when exposed to ultraviolet light. The stabilizers of the present invention are nondiscoloring. They stabilize both the uncured copolymer and the vulcanizate. They are, therefore, advantageously added to the emulsion of the copolymer obtained on emulsion copolymerization so that on. coagulation'they are uniformly distributed in the coagulum and stabilize it during drying and subsequent treatment.

The tin complexes of this invention are produced by reacting stannous chloride or other water-soluble stannous salt of a strong acid, a phenolic compound, and alkali in solution. They are light-colored and, therefore, contain no tin oxide which is a black compound. They contain more tin than calculated for the tin salt of the phenolic compound. Their structure is unknown. They may be tin oxide polymers stabilized by the phenolic compound having a formula such as ROSnOSnOSnOH, Where R is an aromatic residue. One of the terminal hydroxyl in this suggested molecule may to some extent be replaced by chlorine or other acid radicaldepending upon the tin salt used in producing the complex. There is little fact to support such a suggested structure, and it may be far from the actual structure.

The complexes may be produced from a phenolic compound such as:

The stannous-salts used in the preparation of the complexes are stannous salts of strong acids and include stannous chloride, stannous bromide, stannous sulfate, stannous benzene sulfonate, stannous toluene sulfonate, stannous naphthalene sulfonate, etc.

The following examples illustrate the preparation of the complexes:

EXAMPLE 1 'SrANNoUs COMPLEX or PHENOL Twenty grams of sodium hydroxide were dissolved in 200 cubic centimeters of water, and then 4'7 grams of phenol were dissolved in the resulting solution. A solution of 47.4 grams of stannous chloride (anhydrous) in 100 cubic centimeters of water was added slowly during stirring. The precipitate was filtered, washed, and dried at C. The yield was 45.0 grams. The precipitate was white and when heated over an open flame .it decomposed before melting. .It underwent .no apparent change .on heating one 3 hour at 150 C. On analysis, it yielded 61.02 per cent of tin; whereas the calculated content for the normal stannous salt is 38.9 per cent. The chlorine content was 2.66 per cent.

EXAMPLE 2 STANNOUS COMPLEX or BETA-NAPHTHOL Seventy-two grams of beta-naphthol were dissolved in one liter of methanol, and to this was added a solution of 20 grams of sodium hydroxide in 200 cubic centimeters of water. A solution of 47.4 grams of stannous chloride in cubic centimeters of 50 per cent ethanol was then added slowly during stirring. The product was filtered and washed twice with alcohol. It was dried and found to weigh 43.3 grams. It was a. light-cream-colored powder which decomposed before melting on heating to a high temperature. It underwent no apparent change when heated one hour at 150 C. A tin analysis showed it to contain 67.10 per cent tin. The calculated tin content of the normal salt is 29.3 per cent.

EXAMPLE 3 STANNOUS COMPLEX or BETA-NAPHTHOL Thirty-six grams (.25 mol) of beta-naphthol and 56.4 grams of SnCl2.2H2O (.25 mol) were dissolved in 300 cubic centimeters of 95 per cent ethanol. A solution of 20 grams (.5 mol) of sodium hydroxide in 250 cubic centimeters of 50 per cent ethanol was added very slowly during stirring. The product was filtered off, washed with alcohol and water, and then dried. It was a light-cream-colored solid which weighed 40 grams. It decomposed before melting on heating to a high temperature but underwent no apparent change when heated one hour at 150 C. The tin content was 73.10 per cent. The calculated tin content for the normal salt is 29.3 per cent.

EXAMPLE 4 STANNOUS COMPLEX or O-CHLOROPHENOL Sixty-four and one-quarter grams of o-chlorphenol were dissolved in a solution of 20.6 grams of sodium hydroxide in 200 cubic centimeters of water. A solution of 47.4 grams of stannous chloride (anhydrous) in 100 cubic centimeters of water was added to this. An oily precipitate settled to the bottom. It was washed by decantatlon and then separated from the water and dried. It was a white solid which decomposed before melting on heating to a high temperature over an open flame but, apparently, was stable when heated one hour at 150 C. The yield was 55 grams. It was found by analysis to contain 53.45 per cent tin. The calculated tin content of the normal stannous salt is 31.8 per cent.

EXAMPLE 5 STANNOUS COMPLEX or P-PHENYLPHENOL washed twice with 500 cubic centimeter portions of alcohol and once with water. The yield of dried product was 83 grams. It was a very light yellow solid which decomposed on heating to a high temperature on a spatula. It was, apparently, stable when heated one hour at 150 C. It was found to contain 64.15 per cent tin, The calculated tin content of the normal stannous salt is 25.9 per cent. The chlorine content was .36 per cent.

EXAMPLE 6 STANNOUS COMPLEX or P-OYCLOHEXYLPHENOL An alcohol-water solution of 52.8 grams of p-cyclohexylphenol and 24.0 grams of sodium hydroxide was prepared. To this was added, with stirring, a solution of 56.8 grams of stannous chloride (anhydrous) in alcohol. The precipitate was filtered and then washed with alcohol and water. The yield was 52.0 grams. The cream-colored product decomposed before melting when heated over an open fiame. It underwent no apparent change when heated one hour at 150 C. It contained 75.85 per cent tin and 10.3 per cent chlorine. The calculated tin content for the normal salt is 25.3 per cent.

The ortho-dihydroxyphenols, such as catechol, form a compound analyzing close to the normal stannous salt when reacted with equivalent amounts of stannous chloride and alkali. However, the other polyhydroxy aromatic compounds, such as resorcinol, etc., form complexes which are much higher in tin than the normal salt. The following example is illustrative:

EXAMPLE '7 STANNOUS CoMPLEX 0F HYDBOQUINONE Fifty-five grams of hydroquinone and 112.8 grams of stannous chloride dihydrate were dissolved in one liter of water. A solution of 40 grams of sodium hydroxide in 150 cubic centimeters of water was slowly added until the solution was alkaline. This required about 75 per cent of the solution. After stirring a short time, the product was filtered. The yield was 78 grams. The product, a light-cream-colored solid, was, apparently, unchanged by heating one hour at 150 C. It decomposed on heating at a high temperature on a spatula. Analysis for tin showed it to contain 70.45 per cent. It contained 14.75 per cent chlorine. The calculated tin content for the normal salt is 52.3 per cent.

EXAMPLES 8-13 STANNOUS CoMPLExEs or PHENOLS PREPARED BY FoLLowiNe GENERAL METHoD The following general method was employed in producing stannous complexes of:

p-tertiary-octylphenol p-cyclohexylphenol p-tertiary-butylphenol Petroleum cresylic acid 4,6-di-tertiary-butyl-m-cresol 2,6-di-tertiary-butyl-p-cresol Three-tenths of a mol of sodium hydroxide (dissolved in water) was added to .3 mol of the phenol dissolved in per cent ethanol. Then .15 mol (28.4 grams) of anhydrous stannous chloride in ethanol-water was added slowly during stirring. The precipitate was filtered, washed with alcohol and water, and dried.

The complexes thus obtained were light in color and contained more tin than the normal stannous salts of these phenols.

In general, the procedure for the production of the stannous complexes may be given as reaction of the stannous salt with a phenolic compound and up to the equivalent amount of alkali. The amount of phenolic compound used may be varied over wide limits, and there is no harm in using a large excess (much greater than one molecular equivalent) and as little as 0.5 molecular equivalent of the phenol. Examples 3 and 6 illustrate the use of less than a molecular equivalent of phenol. Perhaps less "than 0.5 molecular equivalent of the phenol would be sufficient if of :several' complexes with that of phenyl-beta naphthylamine on drying latex coagulum which contains 2 per cent of stabilizer and also illustrates the stabilizing effect on aging :at elevated temperatures. The table not only shows that the stabilizers are nondiscoloring but also shows that there was no appreciable change in the physical properties of the copolymer on aging. The control containing phenylbeta-naphthylamine showed some deterioration. The data in the table consist of an observation of the color and the results of a hand test. This hand test consisted of pulling and feeling the copolymer sample to detect any stiffening, softening or other signs of deterioration. Tests recorded for the material aged 4 days include a test on the Firestone Extrusion Plastometer described in Dillon .et al. 2,045,548. The figures given are the number-of seconds required to extrude a constant volume of rubber through a given opening by action of a piston activated by a constant pressure of ll- A1 pounds steam at a constant temperature of 185 F.

Table I .-C',0polgmer aging ggg After Four Days at 90 C. After Two Days at 120 C. Antioxidant Color Hand Test T4-l/4 Color Hand Test Color 1 Hand Test stannous complex of white. no deteri- 8.0 light brownl unchanglight brown unchangphenol. oration. ed. ed. stannous complex of 0- .do.. do 8.0 .do do do Do.

chlorcphenol. i stannous complex of p- .do do 6.0 very light do do Do.

phenylphenol. brown. phcnyl-beta-naphthylabrown. ..do 5.6 brown do dark brown. somewhat mine (control). set up.

The data in the above table show the stannous complexes to be equal to phenyl-beta-naphthylamine on aging at 90 C. and superior on aging at 120 C. In color, all of the samples containing the stannous complexes are quite superior to those containing phenyl-beta-naphthylamine. The samples were all coagulated from the copolymerization emulsion mixture by the use of aluminum sulfate low in iron.

The next table compares the stabilizing effect of several of the complexes with that of phenylbeta-naphthylamine when mixed with the emulsion resulting from the copolymerization reaction. Two per cent of the stabilizer was used in each case.

Table II .C'0polymer aging Antioxidant Condition After Drying-Color and Hand Test After Aging 2 Daysat 90 C,- Color and Hand Test After Aging-4 Days at 90 C. Color and Hand 'Test stannous complex of bcta-naphthol (prepared according to the process of Example 2).

stannous complex of beta-naphthol (prepared according to the process of Example 3).

stannous complex 01 4, 6-di-tertiary-' .phenyl-beta-naphthylamine cream color; no deterioration.

light yellow; no

deterioration.

light red-brown;

no deterioration.

cream color; un-

changed.

light brown; un-

changed. brown; unchanged.

light yellow; un-

changed.

crearn color; un-

changed.

light brown; un-

changed.

brown; somewhat set up.

was tested. The vulcanizates were also exposed to ultraviolet light to evaluate their resistance to discoloration. They stabilize without appreciable discoloration. The following tests illustrate the stabilizing effect and particularly as compared with phenyl-beta-naphthylamine, a stabilizer widely used commercially for such .a rubber.

The first table compares the stabilizing effect 75 For convenience, the tests refer to mixtures of Table III.-C'opolymer aging A ntioxidant After Drying Hours at 75 Color and Hand Test Aiter Aging 4 Days at 90 C.Color and Hand Test After Aging 1 Day at 120 C.Color and Hand Test 2% 2,ddi-tertiary-butyl-p-cresol 2% stannous complex of 2,6-di-tertiarybutyl-p-cresol.

1% 2,6-di-tertiary-butyl-p-cresol-l-1% stannous complex of same. 2% stannous complex of beta-naphthol- 1% beta-naphthol-l-IZ, stannous complex of same. heta-naphthol yellow; no deterioration.

light brown; no deterioration.

very light brown; no deterioration.

cream color; no deterioration.

light cream; no deterioration. very light brown;

oran ge-yellow; un-

changed.

light yellowb r 0 w n u n changed.

light brown; un-

changed.

light yellow, un-

changed.

cream, unchanged.

brown; unchanged.

light brown; set up.

light brown; surface slightly resinous.

light brown; un-

changed.

brown; surface somewhat resinous. cream; unchanged.

brown; somewhat no deterioration.

Table IV.-Copolymer aging 2% stannous com- 27 h n a bet plex of hydrop e y a 2% Stalite quinone naphthylamine Condition after drying 20 hours at 37.0 7.8 8.0 light cream brown.-. green-gray.

no deterioration. no deterioration... no deterioration.

18.8 26.4 light brown. brown. Hand test unchanged slightly set up. Heating 4 days at 110 C T4l/4 52.8 309 6. Color light bro\ brown. Hand test unchanged set up.

The above data show that the stannous complex: of hy droquinone is superior to phenylbeta-naphthylamine as a stabilzer for the unstabilizers was added while the copolymer was still in the form of latex and before coagulation and drying.

cured copolymer and show a definite superiority FORMULA I of the stannous complex as compared with Stalite (heptylated diphenylamine), a widely used Copolymer Stabihzer 10o stabilizer for GR-S. Bardol 3 The stabilizers were compounded with vulcan- Pme P 3 izing ingredients according to two formulae. In siearlc ac1d 3 one formula channel black was used, and the Zmc OXlde 5 results of the test with this formula show the Cyclohexyl benzothlazyl $111f6namide 1.2

effect of the presence of the stabilizer in an ordig fii black 50 nary stock. The other formula contains no black and is heavily loaded with zinc oxide, titanium dioxide, and Calcene (a finely divided calcium 1.

carbonate supplied by Pittsburgh Plate Glass Company). Tests with this latter stock show the stabilizers of this invention to be nondiscoloring. In both formulae, GR-S copolymer was employed to which 2 per cent of the various l5 The Bardol of the above formula is a coal-tar plasticizer.

In the following table tests on the physical properties of different vulcanizates are re corded. The values are averages of those obtained on stock cured 60 and minutes, respectively, at 280 F.

anaemia.

Table V.--Properties: oficulcamzate stannous l com lex'of' g fif f' as henol Tensile? Normal 3, 1(10 3; 1-75 Aged 2, 150. 1,875 PerccntofNorm all 69.- 59. l Elongation; I

Normal 585 605 Aged 300- 310 Percent. otINormal 51'. 3 51. 2

The aging was carried" on for hoursin an air bomb at 260 F. under 60' pounds" air pressure. The results ofthe testsshow that compared to phenyl-betanaphthylamine the stannous complex gave better retention of tensile on aging and about the same elongation retention.

The following table records tests on the physical properties of vulcanizates' stabilized with 2' per cent of different stabilizers. The values given are averages of cures obtainedat 280 F. for 40, 60, 80", and 120 minutes, respectively.

The above data; show that, the stabilizer used gives retention of modulus, tensile, and elongation: on. aging: which: comparable to that given by the widely approved phenyl-beta-naphthylamine.

A further test was run to compare the stabilizing effect of a difierent stabilizer with that of phenyl-beta-naphthylamine. Two per cent of each stabilizerwas employed. The values recorded. are the average of. cures made at 280 F; for 80v and 120 minutes, respectively.

Table VII.,Properties of vulcaniaate The results show that the stannous complex is superior to phenyl-beta-naphthylamine from the standpoint of modulus retention and about equivalent in tensile and elongation retention.

In compounding the GR-S for tests in white stock, 2 per cent of various stabilizers was added to latex of GR-S copolymcr before coagulation.

IOI

10 The. dried copolymer was then compounded. as follows:

FORMULAII:

Copolymer+stabilizer Stearic acid 1' Paraffin wax 015 Calc'ene 50 Zinc oxide 5" Titanium dioxide- 8 Sunproof wax 128 Green dye 2 Cumar 2.5 Accelerator #1 123 Accelerator #2" 0.1 Sulfur 1 .5

The Calcene is finely divided. calcium carbonate produced by Pittsburgh Plate Glass Company. Accelerator #1 is cyclohexyl benzothiazyl sulfenamide. Accelerator; #2 is tetramethylthiuram disulfido.

Samples of the white vulcanizate were cured 280 F. for 30 and: 60 minutes, respectively, and then exposed in a Fadeometer for 24 hours at 125 F. with the following, results:

Table VIIL-Vulcani'zate aging Color ofliged Vulcanizate Antioxidant 2% stannous complex of p-pheuyl phenol slightly discolored. 1%2,6-dl-tertiary butylep-oresol 1%;

stannous complex of same very slightly'discolored'.

1% beta-naphthol' 1%stannouscomplex ofsame slightly discolored. 2%stannous complex of hydro uin'one D 2%l1epty-lated.diphenylamine control) di-beta-naphthylwp-phenylene diamine:

(control) 0. light brown.

1 very dark brown.

The stabilizers may be used not only for the stabilization of GR-S and other copolymers of conjugated diene monomer. and vinyl monomer, but also natural rubber, etc. They may beadded to the latex or compounded. on. the mill with dried latex coagulum or crepe, etc. They have particular value as nondiscoloring. stabilizers for white GR-S or other copolymer of a conjugated diene monomer anda vinyl aromatic monomer.

What I claim is:

1. A stannous: complexof a. phenolic compound produced by reaction of the. stannous salt of. a strong acid, a phenolic compound, and alkali, which complex contains more tin. than. the. normal: stannous salt ofv the. phenoliccompound and is light in color, said phenolic compound being from the class consisting of the monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups.

2. A stannous complex of a phenolic compound produced by reaction of stannous chloride, a phenolic compound, and alkali, which complex contains more tin than the normal stannous salt of the phenolic compound and is light in color, said phenolic compound being from the class consisting of the monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups.

3. A light-colored stannous complex produced by reaction of the stannous salt of a strong acid,

a monohydric single-ring phenol, and an alkali, which complex contains more tin than the normal stannous phenolate.

4. A light-colored stannous complex produced by reaction of stannous chloride, 9, monohydric single-ring phenol, and an alkali, which complex contains more tin than the normal stannous phenolate.

5. A light-colored stannous complex produced by reaction of the stannous salt of a strong acid, a naphthol, and an alkali, which complex contains more tin than the normal stannous naphtholate.

6. A light-colored stannous complex prepared by reaction of the stannous salt of a strong acid, a compound from the class consisting of the polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, and an alkali, which complex contains more tin than the normal stannous salt of the polyhydroxy aromatic compound.

7. A light-colored stannous complex prepared by reaction of stannous chloride, a compound from the class consisting of the polyhydroxy aromatic com ounds except those which contain ortho hydroxy groups, and an alkali, which com plex contains more tin than the normal stannous salt of the polyhydroxy aromatic compound.

8. The process of producing a stannous complex which comprises reacting in an aqueous solution (1) a phenolic compound of the class consisting of monohydroxy aromatic compounds and polyhydr'oxy aromatic compounds except those which contain ortho hydroxy groups, (2) the water-soluble stannous salt of a strong acid, and (3) an alkali, thereby producing a light-colored stannous complex which contains more tin than the normal stannous salt of the phenolic compound, the phenolic compound being used in an amount at least equal to that present in said complex, and the amount of alkali being at least substantially one molecular equivalent for each molecular equivalent of stannous salt.

9. The process of producing a stannous complex which comprises reacting (1) a phenolic compound of the class consisting of monohydroxy aromatic compounds and polyhydroxy aromatic compounds except those which contain ortho hydroxy groups, (2) stannous chloride, and (3) n alkali, thereby producing a light-colored stannous complex which contains more tin than the normal stannous salt of the phenolic compound, the phenolic compound being used in an amount at least equal to that present in said complex, and the amount of alkali being at least substantially one molecular equivalent for each molecular equivalent of stannous chloride.

10. The process of producing a stannous complex which comprises reacting in an aqueous solution a monohydric phenol, a water-soluble stannous salt of a strong acid, and an alkali, thereby producing a light-colored stannous complex which contains more tin than the normal stannous phenolate, the phenol being used in an amount at least equal to that present in the complex, and the amount of alkali used being at least substantially one molecular equivalent for each molecular equivalent of the stannous salt.

11. The process of producing a stannous complex which comprises reacting a monohydric phenol, stannous chloride, and an alkali, thereby producing a light-colored stannous complex which contains more tin than the normal stannous phenolate, the phenol being used in an amount at least equal to that present in the complex, and the amount of alkali used being at least substantially one molecular equivalent for each molecular equivalent of stannous chloride.

12. The method of producing a stannous complex which comprises reacting in an aqueous solution a water-soluble stannous salt of a strong acid, an alkali, and a polyhydroxy aromatic compound which contains no ortho hydroxy groups, thereby obtaining a light-colored complex which contains more tin than the normal stannous salt of the polyhydroxy aromatic compound, the phenol being used in an amount at least equal to that present in the complex, and the amount of alkali used being at least substantially one molecular equivalent for each molecular equivalent of the stannous salt.

13. The method of producing a stannous complex which comprises reacting stannous chloride, an alkali, and a polyhydroxy aromatic compound which contains no ortho hydroxy groups, thereby obtaining a light-colored complex Which contains more tin than the normal stannous salt of the polyhydroxy aromatic compound, the phenol being used in an amount at least equal to that present in the complex, and the amount of alkali used being at least substantially one molecular equivalent for each molecular equivalent of stannous chloride.

HARRY E. ALBERT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Freidlina et al., Article in Compt. Rend Acad. Sco. U. R. S. S. 29 (567-) 1940; in Chem. Abs. vol. 35 (3614) 1941. 

1. A STANNOUS COMPLEX OF A PHENOLIC COMPOUND PRODUCED BY REACTION OF THE STANNOUS SALT OF A STRONG ACID, A PHENOLIC COMPOUND, AND ALKALI, WHICH COMPLEX CONTAINS MORE TIN THAN THE NORMAL STANNOUS SALT OF THE PHENOLIC COMPOUND AND IS LIGHT IN COLOR, SAID PHENOLIC COMPOUND BEING FROM THE CLASS CONSISTING OF THE MONOHYDROXY AROMATIC, COMPOUNDS AND POLYHYDROXY AROMATIC COMPOUNDS EXCEPT THOSE WHICH CONTAIN ORTHO HYDROXY GROUPS. 